1. Field of the Invention
The present invention relates to a convergence adjusting apparatus for a color display, and more particularly to a convergence adjusting apparatus for a front or rear projection television in which electron guns corresponding to the colors R, G and B are used.
2. Description of the Related Background Art
There is known a convergence adjusting apparatus for a color display which effects convergence adjustment for each of the adjustment points on a display.
FIG. 1 shows an example of the structure of such a prior art convergence adjusting apparatus.
In FIG. 1, an H-period basic waveform generator 1 generates a basic waveform signal A1 for the zero order component of a convergence signal (hereinafter referred to as "Conver. zero order") which is the DC component of the convergence signal, a basic waveform signal A2 for Convergence 1st order which is the first order component of the convergence signal, and a basic waveform signal A3 for Convergence second order which is the second order component, as shown in FIG. 2. These signals are supplied to a multiplier 2. The basic waveform signal A1 is a direct current signal having a predetermined level. The basic waveform signal A2 is a sawtooth waveform signal having a period equal to one horizontal scan period. The basic waveform signal A3 is a parabolic waveform signal having a period corresponding to one horizontal scan period.
A V-period basic waveform generator 3 generates a basic waveform signal B1, a basic waveform signal B2 and a basic waveform signal B3, as shown in FIG. 2, and supplies these signals to the multiplier 2. The basic waveform signal B1 is a direct current signal having a predetermined level. The basic waveform signal B2 is a sawtooth waveform signal having a period corresponding to one vertical scan period. The basic waveform signal B3 is a parabolic waveform signal having a period corresponding to one vertical scan period.
The multiplier 2 multiplies the basic waveform signals A1 to A3 and the basic waveform signals B1 to B3 together as described below to obtain waveform signals C1 to C9 for adjustment (hereinafter referred to as "adjustment-use waveform signals C1 to C9") and supplies the adjustment-use waveform signals to a level adjusting circuit 4.
(A1).times.(B1)=(C1) PA0 (A1).times.(B2)=(C2) PA0 (A1).times.(B3)=(C3) PA0 (A2).times.(B1)=(C4) PA0 (A2).times.(B2)=(C5) PA0 (A2).times.(B3)=(C6) PA0 (A3).times.(B1)=(C7) PA0 (A3).times.(B2)=(C8) PA0 (A3).times.(B3)=(C9)
The level adjusting circuit 4 independently adjusts the levels of the adjustment-use waveform signals C1 to C9 in accordance with convergence adjusting signals supplied by a control circuit 5, and supplies resultant adjustment-use waveform signals D1 to D9 to an adder 6.
FIG. 3 shows the internal structure of the level adjusting circuit 4.
As shown in FIG. 3, the level adjusting circuit 4 comprises nine independent level adjusting devices 41 to 49, which are supplied with the above-mentioned adjustment-use waveform signals C1 to C9, respectively, as inputs. These level adjusting devices 41 to 49 adjust individual levels of the adjustment-use waveform signals C1 to C9 by amounts corresponding to the levels of convergence adjusting signals supplied by the control circuit 5, and they supply resultant adjusting waveform signals D1 to D9 to the adder 6.
The adder 6 adds up the adjusting waveform signals D1 to D9 to obtain a composite waveform signal and supplies the signal to an amplifier 7. The amplifier 7 amplifies the composite waveform signal as required and supplies a resultant amplified signal to a convergence deflection yoke 8.
Final levels of the convergence adjusting signals supplied to the level adjusting devices 41 to 49 at the time of completion of convergence adjustment, i.e. values indicating the levels of last supplied convergence adjusting signals to the level adjusting devices 41 to 49 are stored in a memory 9. After completion of convergence adjustment, the levels of convergence adjusting signals stored in the memory 9 are supplied to the corresponding level adjusting devices 41 to 49, respectively, for correction of convergence.
Independent convergence deflection yokes are provided for adjusting horizontal and vertical components, respectively, and also for adjusting a red component, a green component and a blue component (hereinafter referred to as R, G and B, respectively). Hence, each color display is provided with a total of six convergence adjusting apparatuses, each having the structure shown in FIG. 1.
In a convergence adjusting apparatus having the aforementioned structure, the current supplied to each convergence deflection yoke is changed by gradually changing the levels of the above-mentioned convergence adjusting signals, thereby moving beam spots of R, G and B irradiated on a display so as to converge to one spot and thus effecting convergence adjustment.
FIGS. 4A to 4I illustrate the fashion in which beam spots irradiated on the display move in accordance with a change in the levels of convergence adjusting signals. FIGS. 4A to 4I show effects of adjusting operations for the horizontal component.
For example, when the level of the convergence adjusting signal supplied to the level adjusting device 41 is shifted, beam spots move toward the right side of a display over the entire surface thereof, as shown in FIG. 4A. When the level of a convergence adjusting signal supplied to the level adjusting device 42 is shifted, beam spots in the upper portion of the display move to the right side thereof, and beam spots in the lower portion of the display move toward the left side thereof, as shown in FIG. 4B. When the level of a convergence adjusting signal supplied to the level adjusting device 43 is shifted, beam spots in the central portion of the display remain still and beam spots in the upper and lower portions of the display move toward the right side thereof, as shown in FIG. 4C.
As described above, convergence adjusting signals are selectively supplied to level adjusting devices for moving beam spots, thereby adjusting convergence such that beam spots of R, G and B converge at one spot for each of nine adjustment points P0 to P8 on the display shown in FIG. 5.
However, in an adjusting operation with such a convergence adjusting apparatus, adjustment for one adjustment point causes all beam spots on the display to concurrently move, as illustrated in FIGS. 4A to 4I. For example, when adjustment is effected for an adjustment point P7 after adjustment for an adjustment point P6 in FIG. 5 has been completed, the beam spot at the adjustment point P6 moves again, thus requiring another adjustment for the adjustment point P6. In other words, adjustment for each adjustment point must be performed while predicting how other beam spots at other adjustment points move.
Therefore, the conventional convergence adjustment requires skill. Particularly, in the case where convergence adjustment is performed at a place where a color display has been installed after shipment, it is necessary for an adjuster to pay attention to the movement of all other adjustment points when effecting adjustment of a certain adjustment point. Therefore, convergence adjustment requires a prolonged time and is not easy.